Power supply unit and power supply system having the same

ABSTRACT

Each of power supply units in a power supply system according to the present invention includes a power supply module, a voltage increase/decrease circuit for increasing the voltage across the power supply module and outputting the increased voltage to a load, and a control circuit. The control circuit calculates the power of the power supply module on the basis of the voltage across the power supply module and current flowing in the power supply module, outputs the power calculation result to a control circuit of another power supply unit, and generates and outputs a control signal to the voltage increase/decrease circuit on the basis of a target output voltage of the voltage increase/decrease circuit, the power calculation result, and a power calculation result obtained from a control circuit of a third power supply unit.

This application is based on Japanese Patent Application No. 2003-313422filed on Sep. 5, 2003 and Japanese Patent Application No. 2004-090798filed on Mar. 26, 2003, the contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply unit and a power supplysystem having a secondary cell or the like to/from which power can beinput/output. More particularly, the present invention relates to apower supply unit and a power supply system realizing efficient paralleldriving of secondary cells or the like.

2. Description of the Prior Art

Hitherto, as a power supply to/from which power can be input/output, asecondary cell (storage battery) and a capacitor are used. As secondarycells, there are known a battery pack in which a plurality of secondarycells are connected in series with one another and a battery pack inwhich a plurality of secondary cells are connected in parallel with eachother. There is also generally known a method of increasing electricenergy which can be continuously output by connecting a plurality ofcapacitors in parallel with one another.

In a power supply system constructed by connecting a plurality ofconverters in parallel, there are known a method of calculating anaverage value of output currents of the plurality of converters andadjusting output current of each of the converters to the calculatedaverage output current and a method of detecting the maximum outputcurrent from output currents of the plurality of converters andadjusting output current of each of the converters to the detectedmaximum output current. Such methods are disclosed in, for example,Japanese Patent No. 2833460 and “Parallel Drive Control of DC-DCConverters” (The Institute of Electronics, Information and CommunicationEngineers, issued in November, 1992, IEICE Technical Report, PE92-47,pp. 23-29).

On the other hand, in recent years, a fuel cell using hydrogen as amaterial is being actively developed. FIG. 9 is a diagram showing outputcharacteristics of a fuel cell. A solid line 300 indicates an outputcharacteristic of a fuel cell in the case where the horizontal axisdenotes output current and the vertical axis indicates output voltage.As shown by the solid line 300, the fuel cell has the characteristicthat as the output of current increases, the output voltage decreases.As understood from a solid line 301 indicating the output characteristicof the fuel cell in the case where the horizontal axis denotes outputcurrent and the vertical axis indicates output power, as the outputcurrent increases from 0 ampere, the output power of the fuel cellincreases. The output power becomes the maximum at current Ij. When theoutput current is increased more than the current Ij, the output powerdecreases. When the current exceeding the current Ij is output, the fuelcell may be destroyed, so that it is necessary to control to always usethe fuel cell at the current Ij or less.

For example, in the case of using, as a power supply, a battery pack inwhich “k” (“k”: an integer of 2 or more) secondary cells are connectedin parallel with one another, as compared with the case of using asingle secondary cell as a power supply, ideally, constant power can becontinuously supplied to a load for time which is long by “k” times(that is, the life of the power supply increases by “k” times).

In the battery pack in which “k” secondary cells are connected inparallel with one another, however, even if the capacities of the “k”secondary cells are the same, current flowing in the secondary cellsvaries due to variations in the internal resistance of the secondarycells. As a result, the powers generated at both ends (both poles) ofthe secondary cell (the product between voltage across the ends (bothpoles) of the secondary cell and current flowing in the secondary cell)also varies. Consequently, the time points at which the residualquantities of the secondary cells become zero and the time points atwhich the secondary cells are fully charged are different from oneanother. Therefore, actually, it does not mean that by using the batterypack, the life of the power supply increases by “k” times (actually, thelife increases less than “k” times).

This phenomenon similarly occurs also in the case of using capacitors inplace of secondary cells. Further, there is another problem in that asecondary cell having low internal resistance is over-discharged orover-charged and the characteristics of the secondary cell deteriorate.

Also in the case where a power supply is constructed by connecting “k”fuel cells in parallel with one another, current flowing in the fuelcells varies due to variations of output impedances of the fuel cells.In this case, current is output preferentially from a fuel cell havinglow output impedance, so that the output current of the fuel cell havinglow output impedance exceeds the current Ij (FIG. 9) and a problemoccurs such that the fuel cell is destroyed.

SUMMARY OF THE INVENTION

In view of the above circumstances, an object of the present inventionis to provide a power supply system capable of adjusting powers obtainedfrom power supply modules of a plurality of power supply units connectedin parallel with one another, and a power supply unit used for the powersupply system.

First Power Supply System: W Balance

In order to achieve the object, a first power supply system according tothe present invention includes a pair of connection terminals to which aload is to be connected, and includes a plurality of power supply unitsconnected in parallel with one another with respect to the pair ofconnection terminals, and each of the power supply units has a powersupply module capable of outputting power. Each of the power supplyunits includes: a voltage detection circuit for detecting a voltageacross the power supply module of the power supply unit itself, acurrent detection circuit for detecting current flowing in the powersupply module of the power supply unit itself, a voltage adjustmentcircuit for increasing the voltage across the power supply module of thepower supply unit itself and outputting the increased voltage to thepair of connection terminals; and a control circuit for controllingoperation of the voltage adjustment circuit. Control circuits of all ofthe power supply units being connected to each other or in an annularshape. In each of the power supply units, the control circuit includes:a power calculation portion for calculating the magnitude of a powergenerated across the power supply module in the power supply unit on thebasis of a result of detection of the voltage detection circuit in thepower supply unit and a result of detection of the current detectioncircuit in the power supply unit; an output portion for outputting apower calculation result of the power calculation portion to a controlcircuit connected; and a control portion for generating a control signalon the basis of a target output voltage of the voltage adjustmentcircuit in the power supply unit, a power calculation result of thepower calculation portion in the power supply unit, and a powercalculation result obtained from the control circuit connected oranother control circuit connected, and for outputting the control signalto the voltage adjustment circuit in the power supply unit.

In the control circuit of each of the power supply units of the firstpower supply system, “in the power supply unit” denotes “in the powersupply unit that incorporates the control circuit”.

In the first power supply system, “power generated across the powersupply module” denotes power output from the power supply module.

The first power supply system according to the present invention isconstructed by connecting two power supply units in parallel with oneanother with respect to the pair of connection terminals, and thecontrol circuits of the two power supply units are connected to eachother. Alternatively, the first power supply system according to thepresent invention is constructed by connecting three or more powersupply units in parallel with one another with respect to the pair ofconnection terminals. The control circuits of all of the power supplyunits are connected in an annular shape by, for example, connecting eachof the control circuits to other two control circuits.

In each of three or more power supply units connected in parallel of thepower supply system, the voltage across the power supply module isdetected by the voltage detection circuit, and current flowing in thepower supply module is detected by the current detection circuit. By thepower calculation portion of the control circuit, a detection result ofthe voltage detection circuit and a detection result of the currentdetection circuit are multiplied with each other, thereby calculatingthe magnitude of power obtained from the power supply module. The powercalculation result is output to one of two control circuits connected toeach other by the output portion.

By the control portion, the control signal is generated on the basis ofthe target output voltage of the voltage adjustment circuit, the powercalculation result, and the power calculation result obtained fromanother control circuit connected. For example, a control signal formaking the output voltage of the voltage adjustment circuit follow thetarget output voltage and setting the difference between the two powercalculation results to zero is generated. The generated control signalis supplied to the voltage adjustment circuit, the voltage across thepower supply module is increased at an increase ratio according to thecontrol signal by the voltage adjustment circuit, and the increasedvoltage is output to the pair of connection terminals.

In such a manner, the control of making the voltage to be output to thepair of connection terminals follow the target output voltage isperformed, thereby setting the voltage to be output to the pair ofconnection terminals.to the target output voltage, and the control formaking the power obtained from the power supply module coincide with thepower obtained from the power supply module of the other power supplyunit connected is executed, thereby equalizing the powers obtained fromthe power supply modules in the two power supply units connected to eachother.

In the first power supply system according to the present invention, asdescribed above, by making the powers obtained from the power supplymodules of two power supply units connected to each other coincide witheach other, the powers obtained from the power supply modules of all ofthe power supply units can be equalized. Therefore, in the case wherethe power supply module is constructed by a secondary cell (storagebattery) or a capacitor, if the capacities of all of the power supplymodules are the same, the residual capacities of all of the power supplymodules become zero at the same time point, and a power supply modulehaving relatively low internal resistance and a power supply modulehaving relatively high output voltage can be prevented from beingover-discharged. In the case where the power supply module isconstructed by a fuel cell, even if the output impedances of fuel cellsare various, all output powers of the power supply modules areequalized. Thus, the risk of destruction of the fuel cell is extremelyreduced.

The first power supply system according to the present invention can beused as a source for supplying power to various loads having differentrated voltages by changing the target output voltage.

The first power supply system according to the present invention can bealso used as a source of supplying power to various loads havingdifferent power consumption by increasing/decreasing the number of powersupply units.

Second Power Supply System: I Balance

A second power supply system according to the present invention includesa pair of connection terminals to which a load is to be connected, andincludes a plurality of power supply units connected in parallel withone another with respect to the pair of connection terminals, and eachof the power supply units has a power supply module capable ofoutputting power. Each of the power supply units comprises: a currentdetection circuit for detecting current flowing in the power supplymodule of the power supply unit itself; a voltage adjustment circuit forincreasing the voltage across the power supply module of the powersupply unit itself and outputting the increased voltage to the pair ofconnection terminals; and a control circuit for controlling operation ofthe voltage adjustment circuit. The control circuits of all of the powersupply units are connected to each other or in an annular shape. In eachpower supply unit, the control circuit includes: an output portion foroutputting a current detection result of the current detection circuitin the power supply unit to a connected control circuit; and a controlportion for generating a control signal on the basis of a target outputvoltage of the voltage adjustment circuit in the power supply unit, thecurrent detection result of the current detection circuit in the powersupply unit, and a current detection result obtained from the controlcircuit connected or another control circuit connected, and foroutputting the control signal to the voltage adjustment circuit in thepower supply unit.

In the control circuit of each of the power supply units of the secondpower supply system, “in the power supply unit” denotes “in the powersupply unit that incorporates the control circuit”.

The second power supply system according to the present invention isconstructed by connecting two power supply units in parallel with oneanother with respect to the pair of connection terminals, and thecontrol circuits of the two power supply units are connected to eachother. Alternatively, the second power supply system according to thepresent invention is constructed by connecting three or more powersupply units in parallel with one another with respect to the pair ofconnection terminals. The control circuits of all of the power supplyunits are connected in an annular shape by, for example, connecting eachof the control circuits to other two control circuits.

In each of three or more power supply units connected in parallel of thepower supply system, the current flowing in the power supply module isdetected by the current detection circuit and, by the output portion ofthe control circuit, the current detection result is output to one ofthe two control circuits connected.

By the control portion, the control signal is generated on the basis ofthe target output voltage of the voltage adjustment circuit, the currentdetection result, and the current detection result obtained from theother control circuit connected. For example, a control signal formaking the output voltage of the voltage adjustment circuit follow thetarget output voltage and setting the difference between the two currentdetection results to zero is generated. The generated control signal issupplied to the voltage adjustment circuit, the voltage across the powersupply module is increased at an increase ratio according to the controlsignal by the voltage adjustment circuit, and the increased voltage isoutput to the pair of connection terminals.

In such a manner, the control of making the voltage to be output to thepair of connection terminals follow the target output voltage isperformed, thereby setting the voltage to be output to the pair ofconnection terminals to the target output voltage, and the control formaking the current flowing in the power supply module coincide with thecurrent flowing in the power supply module of the other power supplyunit connected is executed, thereby equalizing the currents flowing inthe power supply modules in the two power supply units connected to eachother.

In the second power supply system according to the present invention, asdescribed above, by making the currents flowing in the power supplymodules of two power supply units connected to each other coincide witheach other, the currents flowing in the power supply modules of all ofthe power supply units can be equalized. Therefore, in the case wherevariations of the output voltages of the plurality of the power supplymodules are small, the powers obtained from the power supply modulesbecome almost equal to each other. On assumption that variations of theoutput voltages are small, in the where the power supply module isconstructed by a secondary cell (storage battery) or a capacitor, if thecapacities of all of the power supply modules are the same, the residualcapacities of all of the power supply modules become zero at the sametime point, and a power supply module having relatively low internalresistance and a power supply module having relatively high outputvoltage can be prevented from being over-discharged. In the case wherethe power supply module is constructed by a fuel cell, even if theoutput impedances of fuel cells are various, output powers of the powersupply modules are equalized. Thus, the risk of destruction of the fuelcell is extremely reduced.

The second power supply system according to the present invention can beused as a source for supplying power to various loads having differentrated voltages by changing the target output voltage.

Further, the second power supply system according to the presentinvention can be also used as a source of supplying power to variousloads having different power consumption by increasing/decreasing thenumber of power supply units.

Concrete Configuration

In a concrete configuration, each of the power supply modules can alsoreceive power. In each power supply unit, the voltage adjustment circuitdecreases the voltage between the pair of connection terminals andoutputs the decreased voltage to the both ends (both poles) of the powersupply module in the same power supply unit.

In the control circuit of each power supply unit of the concreteconfiguration, “in the same power supply unit” denotes “in the powersupply unit that incorporates the voltage adjustment circuit”.

In the first power supply system having the concrete configuration,“power generated across the power supply module” denotes power outputfrom the power supply module in the case where the power supply moduleoutputs power (at the time of discharging) and denotes power input tothe power supply module in the case where the power supply modulereceives power (at the time of regenerate charging).

In each of the power supply units of the power supply system having theconcrete configuration, at the time of regenerate charging at whichpower is supplied from a load to the power supply module, by the voltageadjustment circuit, the voltage between the pair of connection terminalsis decreased at a decrease ratio according to the control signal fromthe control circuit and the decreased voltage is output across the powersupply module.

In the power supply system having the concrete configuration, at thetime of regenerate charging, the control of making the power to besupplied to the power supply module coincide with the power to besupplied to the power supply module of one of the power supply unitsconnected is performed, thereby equalizing the powers supplied to thepower supply modules between the two power supply units connected toeach other. Thus, the powers supplied to the power supply modules of allof the power supply units are equalized. If the residual capacities ofall of the power supply modules are the same, all of the power supplymodules are fully charged at the same time point, and a power supplymodule having relatively low internal resistance and a power supplymodule having relatively high output voltage can be prevented from beingover-charged.

In a concrete configuration, each of the power supply units has a pairof power input/output terminals connected to the pair of connectionterminals. The voltage adjustment circuit includes: an inductor providedfor one of two serial lines extending from both ends of a power supplymodule to the pair of power input/output terminals; a switching elementfor charging provided on a power input/output terminal side of theinductor of the one serial line and having a rectifier for setting acurrent direction at the time of discharging of the power supply moduleto a forward direction; and a switching element for discharging providedfor parallel lines for connecting the two serial lines to each otherbetween the inductor and the switching element for charging and having arectifier for setting the current direction at the time of charging thepower supply module to a forward direction. The control portion of thecontrol circuit generates a control signal for the switching element forcharging and a control signal for the switching element for discharging.

In each of the power supply units of the power supply system having theconcrete configuration, at the time of discharging when power issupplied from the power supply module to a load, in a state where theswitching element for discharge is on and the switching element forcharging is off, energy is accumulated in the inductor by the voltageacross the power supply module. After that, when the switching elementfor discharging is switched to the off state and the switching elementfor charging is switched to the on state, the energy accumulated in theinductor is supplied to the load via the conductive electrodes of theswitching element for charging and via the rectifier. In such a manner,the voltage increasing operation of increasing the voltage across thepower supply module and outputting the increased voltage to the pair ofconnection terminals is executed.

On the other hand, at the time of regenerate charging when power issupplied from the load to the power supply module, in a state where theswitching element for charging is on and the switching element fordischarging is off, energy generated in the load is supplied to thepower supply module via the inductor. After that, when the switchingelement for charging is switched to the off state and the switchingelement for discharging is switched to the on state, current is passedvia the conductive electrodes of the switching element for dischargingand via the rectifier, and the energy accumulated in the inductor iscancelled. In such a manner, the voltage decreasing operation ofdecreasing the voltage between the pair of connection terminals andoutputting the decreased voltage across the power supply module isexecuted.

In the power supply system having the concrete configuration, the powersupply unit can be made smaller as compared with the configuration wherea voltage increase circuit and a voltage decrease circuit are provided.

Further, in the concrete configuration, a charging power supply forsupplying power to the power supply modules of the plurality of powersupply units can be connected to the pair of connection terminals. Eachof the power supply units has a charging control portion for generatingand outputting a control signal to a voltage adjustment circuit in thepower supply unit itself on the basis of target input current of thepower supply module in the power supply unit itself and a detectionresult of the current detection circuit in the power supply unit itselfwhen the charging power supply is connected to the pair of connectionterminals.

In each of the power supply units of the power supply system having theconcrete configuration, at the time of normal charging when power issupplied from the charging power supply to the power supply module, acontrol signal for making the current flowing in the power supply modulefollow the target input current is generated by the charge controlcircuit, thereby controlling the current flowing in the power supplymodule. Therefore, a conventional charger having the charge controlcircuit is unnecessary.

In another concrete configuration, a charging power supply for supplyingpower to the power supply modules of the plurality of power supply unitscan be connected to the pair of connection terminals. The controlcircuit of each power supply unit has a charge control portion forgenerating and outputting a control signal to the voltage adjustmentcircuit in the power supply unit on the basis of the target inputcurrent of the power supply module in the power supply unit and thedetection result of the current detection circuit in the power supplyunit when the charging power supply is connected to the pair ofconnection terminals.

In each of the power supply units of the power supply system having theconcrete configuration, at the time of normal charging when power issupplied from the charging power supply to the power supply module, acontrol signal for making the current flowing in the power supply modulefollow the target input current is generated by the control circuit,thereby controlling the current flowing in the power supply module.Therefore, a conventional charger having the charge control circuit isunnecessary. As compared with the configuration where a control circuitfor performing discharging control and a control circuit for performingcharging control are provided, the power supply unit can be madesmaller.

For example, the power supply module is constructed by a storagebattery, a capacitor, or a fuel cell. More concretely, the power supplymodule from which power can be output is constructed by a storagebattery, a capacitor, or a fuel cell. A power supply module to/fromwhich power can be input/output is constructed by n storage battery or acapacitor.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an electric configuration of a power supplyunit and a power supply system according to a first embodiment of thepresent invention;

FIG. 2 is a diagram showing an electric configuration of the powersupply unit in FIG 1;

FIG. 3 is a diagram showing an electric configuration of adischarge/regenerate control circuit in FIG. 2;

FIG. 4 is a diagram showing an electric configuration of a chargecontrol circuit in FIG. 2;

FIG. 5 is a diagram showing an electric configuration of a power supplyunit according to a second embodiment of the present invention;

FIG. 6 is a diagram showing an electric configuration of a controlcircuit in FIG. 5;

FIG. 7 is a diagram showing an electric configuration of a power supplyunit according to a third embodiment of the present invention;

FIG. 8 is a diagram showing an electric configuration of a power supplyunit according to a fifth embodiment of the present invention; and

a diagram showing output characteristics of a fuel cell applied to theprior art and the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment: Cell

A first embodiment of a power supply unit and a power supply systemhaving the power supply unit according to the present invention will bedescribed below with reference to the drawings. FIG. 1 is a diagramshowing an electric configuration of the power supply unit and the powersupply system according to the present invention.

FIG. 1: Power Supply System

As shown in FIG. 1, a power supply system 1 of the embodiment isconstructed by “n” (n: an integer of 3 or more) power supply units U1,U2, U3, ..., and Un connected in parallel with one another, and a pairof connection terminals 2, 2 to which a load (not shown) such as a motorand a charging power supply (not shown) for supplying power to the powersupply units Ul to Un are to be connected. To the pair of connectionterminals 2, 2, “n” power supply units U1 to Un are connected inparallel with one another.

Neighboring two power supply units (power supply units U1 and U2, U2 andU3, . . . , and Un−1 and Un) are connected to each other via a controlsignal line 20, and the power supply units U1 and Un at both ends of theparallel arrangement are connected to each other via the control signalline 20, thereby connecting all of the power supply units U1 to Un in anannular shape.

Each of all of the power supply units U1 to Un has one power supplymodule (not shown in FIG: 1). To one of the pair of power supply units,from the other power supply unit connected via the control signal line20, a calculation result of power generated across the power supplymodule of the one power supply unit is supplied as a power instructionWref to adjust so that the power generated across the power supplymodule of the one power supply unit coincides with the power instructionWref.

In the embodiment, to the power supply unit U1, a result of calculationof power generated at both ends of the power supply module of the powersupply unit U2 is given as the power instruction Wref from the powersupply unit U2. To the power supply unit U2, a result of calculation ofpower generated at both ends of the power supply module of the powersupply unit U3 is given as the power instruction Wref from the powersupply unit U3. In such a manner, the powers generated across the powersupply modules are adjusted between two neighboring power supply unitsand between the power supply units U1 and Un at both ends, therebymaking the powers of all of the power supply modules uniform.

FIG. 2: Description of Configuration

FIG. 2 shows the configuration of the power supply unit U1. Since theconfiguration of the power supply units U2 to Un other than the powersupply unit U1 is similar to that of the power supply unit U1, itsillustration and description are omitted. The power supply unit U1 has apair of input/output terminals 11, 11 connected to the pair ofconnection terminals 2, 2(FIG 1). The power supply module 10 isconstructed by either a single secondary cell (storage battery) or aplurality of secondary cells connected in series with one another. Thepair of input/output terminals 11, 11 are terminals to/from (intended tomean “to or from”) which power is input/output (intended to mean “inputor output”), so that they can be also called power input/outputterminals.

For simplicity of description, it is assumed that all of the powersupply modules 10 are charged so as to be able to output the same power.Specifically, when the power supply modules 10 start outputting the samepower simultaneously, the residual quantities of all of the power supplymodules 10 become zero at the same time (the power supply modules 10simultaneously become unable to output the power).

Two serial lines 12, 12 extend from both ends of the power supply module10 (or “both electrodes” there of, since the power supply module 10 isconstructed by a secondary cell) toward the pair of input/outputterminals 11, 11. For the serial lines 12, 12, a voltageincrease/decrease circuit 13 is provided.

The voltage increase/decrease circuit 13 increases the voltage acrossthe power supply module 10 at the time of discharge when power issupplied from the power supply module 10 to a load and outputs theincreased voltage to the pair of input/output terminals 11, 11. On theother hand, the voltage increase/decrease circuit 13 decreases thevoltage between the pair of input/output terminals 11, 11 and outputsthe decreased voltage across the power supply module 10 at the time ofregenerative charging when the power is supplied from the load to thepower supply module 10 and at the time of normal charging when power issupplied from a power supply for charging to the power supply module 10.

For one of the two serial lines 12, 12 (the positive voltage side of thepower supply module 10), a coil 131 as an inductor and a switchingelement 133 for charging constructed by an MOSFET (metal oxidesemiconductor field effect transistor) and a diode having an anode onthe power supply module 10 side thereof are provided. For parallel linesfor connecting the two serial lines 12, 12 on the power supply module 10side of the coil 131, a first capacitor 134 is provided. For parallellines for connecting the two serial lines 12, 12 between the coil 131and the switching element 133 for charging, a switching element 132 fordischarging which is constructed by an MOSFET and a diode having acathode on the coil 131 side thereof are provided. Further, for parallellines for connecting the two serial lines 12, 12 on the side of the pairof input/output terminals 11, 11 of the switching element 133 forcharging, a second capacitor 135 is provided.

At the time of discharging, in a state where the MOSFET of the switchingelement 132 for discharge is on and the MOSFET of the switching element133 for charging is off, energy is accumulated in the coil 131 by thevoltage across the power supply module 10. After that, when the MOSFETof the switching element 132 for discharging is switched to the offstate and the MOSFET of the switching element 133 for charging isswitched to the on state, the energy accumulated in the coil 131 issupplied via the source-drain of the MOSFET and the diode as a rectifierthat are provided in the switching element 133 for charging to thesecond capacitor 135 and the load (not shown) connected to theinput/output terminals 11, 11. In such a manner, the voltage increasingoperation is executed.

On the other hand, at the time of regenerate charging and normalcharging, in a state where the MOSFET of the switching element 133 forcharging is on and the MOSFET of the switching element 132 fordischarging is off, energy generated in the load or the energy of thepower supply for charging is supplied to the power supply module 10 viathe coil 131 and charging is performed. After that, when the MOSFET ofthe switching element 133 for charging is switched to the off state andthe MOSFET of the switching element 132 for discharging is switched tothe on state, current is passed via the first capacitor 134 and via thesource-drain of the MOSFET and the diode as a rectifier that areprovided in the switching element 132 for discharging, and the energyaccumulated in the coil 131 is cancelled. In such a manner, the voltagedecreasing operation is executed.

The voltage increase/decrease circuit 13 constructed by the coil 131,the switching element 132 for discharging, the switching element 133 forcharging, the first capacitor 134, and the second capacitor 135 areexample of a voltage adjustment circuit having the function ofincreasing the voltage across the power supply module 10 and outputtingthe increased voltage to the pair of input/output terminals 11, 11 ordecreasing the voltage across the pair of input/output terminals 11, 11and outputting the decreased voltage across the power supply module 10.

To the two serial lines 12, 12, a first voltage detection circuit 14 fordetecting a voltage across the power supply module 10 (which isidentical with the module voltage Vmod described later) and also asecond voltage detection circuit 15 for detecting an output voltage ofthe voltage increase/decrease circuit 13 are connected. Further, to thetwo serial lines 12, 12, a current detection circuit 16 for detecting acurrent in the power supply module 10 (which is identical with themodule current Imod described later) is connected.

The module voltage Vmod detected by the first voltage detection circuit14, the output voltage Vout detected by the second voltage detectioncircuit 15, and the module current Imod detected by the currentdetection circuit 16 are input to a discharge/regenerate control circuit17 built with a microcomputer. The discharge/regenerate control circuit17 calculates power generated across the power supply module 10 on thebasis of the module voltage Vmod which is a result of detection of thefirst voltage detection circuit 14 and the module current Imod which isa result of detection of the current detection circuit 16 at the time ofdischarging and regenerate charging, and outputs the power calculationresult W to the power supply unit Un as the other power supply unitconnected by the control signal line 20. The “power generated across thepower supply module 10” denotes power output from the power supplymodule 10 at the time of discharging and denotes power input to thepower supply module 10 at the time of regenerate charging.

To the discharge/regenerate control circuit 17, the voltage instructionVref indicative of a target output voltage of the voltageincrease/decrease circuit 13 is input from the outside and the powercalculation result is input as the power instruction Wref from the powersupply unit U2 as the other power supply unit connected via the controlsignal line 20.

The discharge/regenerate control circuit 17 compares the output voltageVout with the voltage instruction Vref supplied as described, comparesthe power calculation result W with the power instruction Wref in theown unit and, on the basis of the result of these comparisons, generatesa first PWM signal to the switching element 132 for discharging of thevoltage increase/decrease circuit 13 and a second PWM signal to theswitching element 133 for charging of the voltage increase/decreasecircuit 13. The first and second PWM signals generated in such a mannerare supplied respectively to the switching element 132 for dischargingand the switching element 133 for charging, thereby controlling on/offstates of the switching elements 132 and 133.

As described above, the control is performed to make the output voltageVout of the voltage increase/decrease circuit 13 follow the targetoutput voltage Vref and to set the output voltage Vout of the voltageincrease/decrease circuit 13 to the target output voltage Vref. And alsothe control is performed to make the power generated across the powersupply module 10 coincide with the power generated across the powersupply module of the power supply unit U2 as one of the power supplyunits connected. Thereby adjusting the powers generated across the powersupply modules of the two power supply units U1 and U2 connected to eachother via the control signal line 20. As described above, since all ofthe power supply units U1 to Un are connected in an annular shape, thepowers generated across the power supply modules of the all of the powersupply units U1 to Un are made coincide with each other.

The module voltage Vmod detected by the first voltage detection circuit14 and the module current Imod detected by the current detection circuit16 are input to a charge control circuit 18 built with a microcomputer.To the charge control circuit 18, a charge current instruction Irefindicative of target input current is input from the outside.

At the time of normal charging, the charge control circuit 18 comparesthe module current Imod with the charge current instruction Iref and, onthe basis of the result of comparison, generates the first PWM signalfor the switching element 132 for discharging of the voltageincrease/decrease circuit 13 and the second PWM signal for the switchingelement 133 for charging of the voltage increase/decrease circuit 13.The first and second PWM signals generated as described above aresupplied respectively to the switching element 132 for discharging andthe switching element 133 for charging, and the switching elements 132and 133 are on/off controlled. In such a manner, the control of makingthe module current Imod flowing in the power supply module 10 follow thecharge current instruction Iref is performed so that the module currentImod is set to the target input current Iref That is, the charge controlcircuit 18 has the function of a charge control portion for generatingthe control signals (first and second PWM signals), and outputting thecontrol signals to the voltage increase/decrease circuit 13 at the timeof normal charging.

The charge control circuit 18 detects the full charge state of the powersupply module 10, on the basis of the module voltage Vmod supplied asdescribed above, and at the time point of detecting the full chargestate, stops supply of the PWM signals to the switching element 132 fordischarging and the switching element 133 for charging. As a result,supply of power from the power supply for charging to the power supplymodule 10 is stopped.

FIG. 3: Details of Discharge/Regenerate Control Circuit

FIG. 3 shows the detailed electric configuration of thedischarge/regenerate control circuit 17 in FIG. 2. As described above,the output voltage Vout, detected by the second voltage detectioncircuit 15 and the voltage instruction Vref from the outside aresupplied to a voltage control circuit 171. In the voltage controlcircuit 171, the voltage instruction Vref is subtracted from the outputvoltage Vout, thereby generating a voltage error signal. The voltageerror signal (Vout-Vref) is supplied to an error amplification circuit172.

The module voltage Vmod, detected by the first voltage detection circuit14, and the module current Imod, detected by the current detectioncircuit 16, are supplied to a power calculation circuit 173. The powercalculation circuit 173 multiplies the module voltage Vmod with themodule current Imod to calculate the power generated across the powersupply module 10. Then, the power calculation circuit 173 supplies thepower calculation result W to a power control circuit 174, and to one ofthe power supply units (in FIG. 1, the power supply unit Un) connectedvia the control signal line 20.

The power instruction Wref is supplied from the other power supply unit(in FIG. 1, the power supply unit U2) connected to the power controlcircuit 174. The power calculation result W is subtracted from the powerinstruction Wref, thereby generating a power error signal. The powererror signal (Wref-W) is supplied to the error amplification circuit172.

In the error amplification circuit 172, the power error signal (Wref-W)is subtracted from the supplied voltage error signal (Vout-Vref),thereby generating an error amplification signal. The erroramplification signal is supplied to a PWM (Pulse Width Modulation)control circuit 175. The PWM control circuit 175 subtracts apredetermined delta wave signal from the error amplification signal,thereby generating the first PWM signal, and outputs the first PWMsignal to the switching element 132 for discharging of the voltageincrease/decrease circuit 13 shown in FIG. 2. The first PWM signal issupplied to an inverter circuit 176. The inverter circuit 176 invertsthe polarity of the first PWM signal to generate the second PWM signaland outputs the second PWM signal to the switching element 133 forcharging.

As described above, the discharge/regenerate control circuit 17 has thefunction of a control portion for generating and outputting the firstand second PWM signals, as control signals, to the voltageincrease/decrease circuit 13 on the basis of the output voltage Vout,the voltage instruction Vref indicative of the target output voltage ofthe voltage increase/decrease circuit 13, the power calculation result Wof the power calculation circuit 173, and the power instruction Wrefobtained from the outside.

FIG. 4: Details of Charge Control Circuit

FIG. 4 shows the detailed electric configuration of the charge controlcircuit 18 in FIG. 2. As described above, the module current Imoddetected by the current detection circuit 16 and the charge currentinstruction Iref from the outside are supplied to a current controlcircuit 181. The current control circuit 181 subtracts the chargecurrent instruction Iref from the module current Imod, therebygenerating a current error signal and supplies the current error signal(Imod-Iref) to a PWM control circuit 182.

The PWM control circuit 182 subtracts a predetermined delta wave signalfrom the current error signal (Imod-Iref), thereby generating the firstPWM signal. In a state where a switch 183 is on, the first PWM signal isoutput to the switching element 132 for discharging of the voltageincrease/decrease circuit 13 shown in FIG. 2. The first PWM signal issupplied to an inverter circuit 184. The inverter circuit 184 invertsthe polarity of the first PWM signal, thereby generating the second PWMsignal. In a state where the switch 183 is on, the second PWM signal isoutput to the switching element 133 for charging.

The module voltage Vmod detected by the first voltage detection circuit14 is supplied to a full charge detection circuit 185. The full chargedetection circuit 185 detects a full charge state of the power supplymodule 10 on the basis of the module voltage Vmod. When the full chargestate is detected, the switch 183 is switched to off, and the supply ofthe PWM signal to the switching element 132 for discharging and theswitching element 133 for charging of the voltage increase/decreasecircuit 13 shown in FIG. 2 is stopped.

In the power supply system 1 of the embodiment, as stated above, bymaking the powers generated across the power supply modules 10 coincidebetween two power supply units connected to each other (for example,between the power supply units U1 and U2) at the time of discharging andregenerate charging, the powers generated across the power supplymodules of all of the power supply units can be equalized.

Therefore, when the capacities of all of the power supply modules 10 arethe same (when all of the power supply modules are charged so as to beable to output the same power) on start of driving of the power supplysystem 1, at the time of discharging, the residual quantities of all ofthe power supply modules become zero at the same time so that a powersupply module having relatively low internal resistance and a powersupply module having relatively high output voltage (corresponding tothe module voltage Vmod) can be prevented from being over-discharged. Atthe time of regenerate charging, all of the power supply modules arefully charged at the same time point so that a power supply modulehaving relatively low internal resistance and a power supply modulehaving relatively low output voltage can be prevented from beingover-charged.

The power supply system 1 of the embodiment can be used as a source forsupplying power to various loads having different rated voltages bychanging the target output voltage Vref. In particular, when the load isa motor, the voltage which can be applied to the motor can be freelyset, so that an adjustment range of the speed of rotation of the motorcan be widened.

The power supply system 1 of the embodiment can be also used as a sourceof supplying power to various loads having different power consumptionby increasing/decreasing the number (that is, the number indicated by“n”) of power supply units U1 to Un.

In the power supply system 1 of the embodiment, the power supply unitbecomes smaller as compared with the configuration having a voltageincreasing circuit and a voltage decreasing circuit.

In the power supply system 1 of the embodiment, at the time of normalcharging, the charge control is performed by the charge control circuit18 of each of the power supply units, so that a conventional chargerhaving a charge control circuit is unnecessary.

Charging can be made with a voltage lower than the output voltage Voutof the power supply unit. For example, when the voltage Vmod across thepower supply module 10 is 24 V and the rated voltage of the load(corresponding to the output voltage Vout of the powers supply unit) is48 V, if the output voltage of the charger is a voltage larger than 24 Va little (for example, 30 V), charging can be performed. Conventionally,a voltage (for example, 50 V) larger than the rated voltage of a load isnecessary as an output voltage of the charger, so that the power supplysystem is subjected to various constraints of standards for safety (suchas, for example in Japan, Electrical Appliance and Material Safety Law).The power supply system 1 can be free from such constraints.

Further, the power supply system 1 of the embodiment can supply avoltage according to the output voltage of the power supply module 10across the power supply module 10 at the time of regenerate charging andnormal charging.

Second Embodiment: Modification of Charging Method

A second embodiment of a power supply unit according to the presentinvention and a power supply system having the power supply unit will bedescribed below with reference to the drawings. The power supply systemof the second embodiment has, like the power supply system 1 of thefirst embodiment shown in FIG. 1, “n” power supply units Ua1, Ua2, . . ., and Uan which are connected in parallel with one another (only thepower supply unit Ua1 is shown in FIG. 5 but the other power supplyunits Ua2 to Uan are not shown) and a pair of connection terminals (notshown) to which a load such as a motor and a power supply for chargingfor supplying power to the power supply unit are to be connected. Thatis, the connection relation of the “n” power supply units Ua1, Ua2, . .. , and Uan is similar to that of the “n” power supply units U1, U2, . .. , and Un of the power supply system 1 in the first embodiment.

FIG. 5: Description of Configuration

FIG. 5 shows the configuration of the power supply unit Ua1 of thesecond embodiment. Since the configuration of the power supply units Ua2to Uan other than the power supply unit Ua1 is similar to that of thepower supply unit Ua1, its illustration and description are omitted. Thepower supply unit Ua1 has a pair of input/output terminals 31, 31connected to the pair of connection terminals (not shown). A powersupply module 30 is constructed by either a single secondary cell(storage battery) or a plurality of secondary cells connected in serieswith one another. The power supply module 30 is similar to the powersupply module 10 in the first embodiment.

Two serial lines 32, 32 extend from both ends of the power supply module30 toward the pair of input/output terminals 31, 31. For the seriallines 32, 32, a voltage increase/decrease circuit 33 is provided. Thevoltage increase/decrease circuit 33 has the same configuration as thatof the voltage increase/decrease circuit 13 of the first embodiment andis constructed by a coil 331, a switching element 332 for discharging, aswitching element 333 for charging, a first capacitor 334, and a secondcapacitor 335. Since the operation of the voltage increase/decreasecircuit 33 is the same as that of the voltage increase/decrease circuit13 of the first embodiment, the description will not be repeated.

To the two serial lines 32, 32, a first voltage detection circuit 34 fordetecting a voltage across the power supply module 30 and also a secondvoltage detection circuit 35 for detecting an output voltage of thevoltage increase/decrease circuit 33 are connected. Further, to the twoserial lines 32, 32, a current detection circuit 36 for detectingcurrent flowing in the power supply module 30 is connected.

The module voltage Vmod detected by the first voltage detection circuit34, the output voltage Vout detected by the second voltage detectioncircuit 35, and the module current Imod detected by the currentdetection circuit 36 are input to a control circuit 37 built with amicrocomputer. The control circuit 37 calculates power generated acrossthe power supply module 30 on the basis of the module voltage Vmod andthe module current Imod at the time of discharging and regeneratecharging, and outputs the power calculation result W to one of the powersupply units connected.

To the control circuit 37, the voltage instruction Vref indicative of atarget output voltage of the voltage increase/decrease circuit 33 isinput from the outside and the power calculation result is input as thepower instruction Wref from the other power supply unit connected.

The control circuit 37 compares the output voltage Vout with the voltageinstruction Vref supplied as described above, compares the powercalculation result W in the own unit with the power instruction Wrefand, on the basis of the results of comparison, generates the first andsecond PWM signals. The first and second PWM signals generated in such amanner are supplied to the switching element 332 for discharging and theswitching element 333 for charging, respectively, of the voltageincrease/decrease circuit 33, thereby controlling on/off states of theswitching elements 332 and 333.

As described above, the control is performed to make the output voltageVout of the voltage increase/decrease circuit 33 follow the targetoutput voltage Vref to set the output voltage Vout of the voltageincrease/decrease circuit 33 to the target output voltage Vref, and thecontrol is performed to make the power generated across the power supplymodule 30 coincide with the power generated across the power supplymodule of one of the power supply units connected, thereby equalizingthe powers generated across the power supply modules of the two powersupply units connected to each other.

To the control circuit 37, a charge current instruction Iref indicativeof target input current is input from the outside.

At the time of charging, the control circuit 37 compares the suppliedmodule current Imod with the charge current instruction Iref and, on thebasis of the result of comparison, generates the first and second PWMsignals. The first and second PWM signals generated as described aboveare supplied to the switching element 332 for discharging and theswitching element 333 for charging, respectively, of the voltageincrease/decrease circuit 33 and the switching elements 332 and 333 areon/off controlled. In such a manner, the control of making the modulecurrent Imod flowing in the power supply module 30 follow the chargecurrent instruction Iref is performed so that the module current Imod isset to the target input current Iref. That is, the control circuit 37also has the function of a charge control portion for generating andoutputting the control signals (first and second PWM signals) to thevoltage increase/decrease circuit 33 at the time of normal charging.

The control circuit 37 detects the full charge state of the power supplymodule 30 on the basis of the module voltage Vmod supplied as describedabove and, on detection of the full charge state, stops supply of thePWM signals to the switching element 332 for discharging and theswitching element 333 for charging. As a result, supply of power fromthe power supply for charging to the power supply module 30 is stopped.

FIG. 6: Details of Control Circuit

FIG. 6 shows the detailed electric configuration of the control circuit37 in FIG. 5. As described above, the output voltage Vout detected bythe second voltage detection circuit 35 and the voltage instruction Vreffrom the outside are supplied to a voltage control circuit 371. In thevoltage control circuit 371, the voltage instruction Vref is subtractedfrom the output voltage Vout, thereby generating a voltage error signal.The voltage error signal (Vout-Vref) is supplied to an erroramplification circuit 372.

The module voltage Vmod detected by the first voltage detection circuit34 is supplied to a power calculation circuit 373 and also to a fullcharge detection circuit 370. The module current Imod detected by thecurrent detection circuit 36 is supplied to the power calculationcircuit 373 and also to a current control circuit 379.

The power calculation circuit 373 multiplies the module voltage Vmodwith the module current Imod to thereby calculate the power generatedacross the power supply module Ua1. The power calculation result W issupplied to a power control circuit 374 and is also output to one of thepower supply units connected.

The power instruction Wref is supplied from the other connected powersupply unit to the power control circuit 374. The power calculationresult W is subtracted from the power instruction Wref, therebygenerating a power error signal. The power error signal (Wref-W) issupplied to the error amplification circuit 372.

In the error amplification circuit 372, the power error signal (Wref-W)is subtracted from the supplied voltage error signal (Vout-Vref),thereby generating an error amplification signal. A first switch 375 isswitched to the error amplification circuit 372 side at the time ofdischarging and regenerate charging, and the error amplification signalis supplied to a PWM control circuit 376 via the first switch 375. ThePWM control circuit 376 subtracts a predetermined delta wave signal fromthe error amplification signal, thereby generating the first PWM signal.In the state where a second switch 377 is on, the first PWM signal isoutput to the switching element 332 for discharging of the voltageincrease/decrease circuit 33 shown in FIG. 5. The first PWM signal isalso supplied to an inverter circuit 378. The inverter circuit 378inverts the polarity of the first PWM signal to generate the second PWMsignal. In a state where the second switch 377 is on, the second PWMsignal is output to the switching element 333 for charging.

That is, the error amplification circuit 372, PWM control circuit 375,and inverter circuit 376 generate and output the first and second PWMsignals as control signals to the voltage increase/decrease circuit 33on the basis of the output voltage Vout, the voltage instruction Vrefindicative of the target output voltage of the voltage increase/decreasecircuit 33, the power calculation result W of the power calculationcircuit 373, and the power instruction Wref obtained from the outside.

The charge current instruction Iref from the outside is supplied to thecurrent control circuit 379. The control circuit 379 subtracts thecharge current instruction Iref from the module current Imod supplied asdescribed above, thereby generating a current error signal. The firstswitch 375 is switched to the current control circuit 379 side at thetime of normal charging, and the current error signal (Imod-Iref) issupplied to the PWM control circuit 376 via the first switch 375. ThePWM control circuit 376 subtracts a predetermined delta wave signal fromthe current error signal, thereby generating the first PWM signal. In astate where the second switch 377 is on, the first PWM signal is outputto the switching element 332 for discharging of the voltageincrease/decrease circuit 33 shown in FIG. 5. The first PWM signal issupplied to the inverter circuit 378. The inverter circuit 378 invertsthe first PWM signal, thereby generating the second PWM signal. In astate where the second switch 377 is on, the PWM signal is output to theswitching element 333 for charging.

The full charge detection circuit 370 detects a full charge state of thepower supply module 30 on the basis of the module voltage Vmod suppliedas described above. When the full charge state is detected, the secondswitch 377 is switched to off, and the supply of the PWM signal to theswitching element 332 for discharging and the switching element 333 forcharging of the voltage increase/decrease circuit 33 is stopped.

In the power supply system of the embodiment, as stated above, by makingthe powers generated across the power supply modules 30 coincide witheach other between two power supply units connected to each other (forexample, between the power supply units Ua1 and Ua2) at the time ofdischarging and regenerate charging, the powers generated across thepower supply modules of all of the power supply units can be equalized.

Therefore, when the capacities of all of the power supply modules 30 arethe same (when all of the power supply modules are charged so as to beable to output the same power) on start of driving of the power supplysystem of the embodiment, at the time of discharging, the residualquantities of all of the power supply modules become zero at the sametime so that a power supply module having relatively low internalresistance and a power supply module having relatively high outputvoltage can be prevented from being over-discharged. At the time ofregenerate charging, all of the power supply modules are fully chargedat the same time point so that a power supply module having relativelylow internal resistance and a power supply module having relatively lowoutput voltage can be prevented from being over-charged.

The power supply system of the embodiment can be used as a source forsupplying power to various loads having different rated voltages bychanging the target output voltage Vref In particular, when the load isa motor, the voltage which can be applied to the motor can be freelyset, so that an adjustment range of the speed of rotation of the motorcan be widened.

The power supply system of the embodiment can be also used as a sourceof supplying power to various loads having different power consumptionby increasing/decreasing the number (that is, the number indicated by“n”) of power supply units Ua1 to Uan.

In the power supply system of the embodiment, at the time of normalcharging, the charge control is performed by the charge control circuit37 of each of the power supply units, so that a conventional chargerhaving a charge control circuit is unnecessary.

Further, in the power supply system of the embodiment, as compared withthe configuration where a control circuit for performingdischarge/regenerate charge control and a control circuit for performingnormal charge control are provided, the power supply unit is smaller.

Charging can be made with a voltage lower than the output voltage Voutof the power supply unit. For example, when the output voltage of thepower supply module 30 is 24 V and the rated voltage of the load(corresponding to the output voltage Vout of the powers supply unit) is48 V, if the output voltage of the charger is a voltage larger than 24 Va little (for example, 30 V), charging can be performed. Conventionally,a voltage (for example, 50 V) larger than the rated voltage of a load isnecessary as an output voltage of the charger, so that the power supplysystem is subjected to various constraints of standards for safety (suchas, for example in Japan, Electrical Appliance and Material Safety Law).The power supply system of the embodiment can be free from suchconstraints.

Third Embodiment: Capacitor

A third embodiment of a power supply unit according to the presentinvention and a power supply system having the power supply unit will bedescribed below with reference to the drawings. The power supply systemof the third embodiment has, like the power supply system 1 of the firstembodiment shown in FIG. 1, “n” power supply units Ub1, Ub2, . . . , andUbn which are connected in parallel with one another (only the powersupply unit Ub1 is shown in FIG. 7 but the other power supply units Ub2to Ubn are not shown) and a pair of connection terminals (not shown) towhich a load such as a motor and a power supply for charging forsupplying power to the power supply unit are to be connected. That is,the connection relation of the “n” power supply units Ub1, Ub2, . . . ,and Ubn is similar to that of the “n” power supply units U1, U2, . . . ,and Un of the power supply system 1 in the first embodiment.

FIG. 7: Description of Configuration

FIG. 7 shows the configuration of the power supply unit Ub1 of the thirdembodiment. Since the configuration of the power supply units Ub2 to Ubnother than the power supply unit Ub1 is similar to that of the powersupply unit Ub1, its illustration and description are omitted. In FIG.7, the same components are given the same reference numerals as those ofFIG. 2 and their description will not be repeated. The power supply unitUb1 in FIG. 7 is similar to the power supply unit U1 in FIG. 2 exceptthat the power supply module 10 in FIG. 2 is replaced with a powersupply module 40. The power supply module 40 is not a secondary cell butis constructed by a single capacitor (hereinafter, referred to as apower capacitor) (obviously, the power supply module 40 may beconstructed by using a plurality of power capacitors). In the case wherethe power capacitor has a polarity, it is sufficient to connect thepositive pole side to the serial line 12 on the coil 131 side.

For simplicity of description, it is assumed that all of the powersupply modules 40 are charged so as to be able to output the same power.Specifically, when the power supply modules 40 start outputting the samepower simultaneously, the residual quantities of all of the power supplymodules 40 become zero at the same time (the power supply modules 40simultaneously become unable to output the power).

Discharging, regenerate charging, and normal charging operations similarto those of the first embodiment are performed. Specifically, in amanner similar to the first embodiment, at the time of discharging andregenerate charging, by making the powers generated across the powersupply modules 40 coincide with each other between two power supplyunits connected to each other (for example, between the power supplyunits Ub1 and Ub2), the powers generated across the power supply modulesof all of the power supply units can be equalized.

Therefore, when the capacities of all of the power supply modules 40 arethe same (when all of the power supply modules are charged so as to beable to output the same power) on start of driving of the power supplysystem of the third embodiment, at the time of discharging, the residualquantities of all of the power supply modules become zero at the sametime so that a power supply module having relatively low internalresistance and a power supply module having relatively high outputvoltage (corresponding to the module voltage Vmod) can be prevented frombeing over-discharged (for example, such a power supply module can beprevented from being unable to output before the other power supplymodules). At the time of regenerate charging, all of the power supplymodules are fully charged at the same time point so that a power supplymodule having relatively low internal resistance and a power supplymodule having relatively low output voltage can be prevented from beingover-charged (for example, a voltage across such a power supply modulecan be prevented from exceeding a predetermined voltage).

As described above, also in the case where the power supply module 40 isconstructed by a power capacitor, nothing is changed from the firstembodiment for the load and the power supply for charging connected tothe pair of connection terminals (not shown in the third embodiment).Therefore, the power supply system of the third embodiment can realizeactions and effects similar to those of the power supply system 1 in thefirst embodiment. Obviously, the third embodiment can be combined withthe second embodiment.

Fourth Embodiment: Combination of Secondary Cell and Capacitor

In the first embodiment, the example of constructing the power supplysystem by the power supply units U1 to Un each having the power supplymodule 10 which is constructed by a secondary cell has been described.In the third embodiment, the example of constructing the power supplysystem by the power supply units Ub1 to Ubn each having the power supplymodule 40 which is constructed by a power capacitor has been described.

In a fourth embodiment of a power supply unit and a power supply systemhaving the power supply unit according to the present invention, a partof the power supply units U1 to Un and a part of the power supply unitsUb1 to Ubn mixedly exist (not shown). For example, in FIG. 1, the powersupply unit U1 having a secondary cell is replaced with the power supplyunit Ub1 having a power capacitor.

Even if such replacement is made, the operation of discharging,regenerate charging, and normal charging in each of the power supplyunits are the same as those of the first embodiment. Consequently,discharging, regenerative charging, and normal charging operationssimilar to those of the first embodiment are performed in all of thepower supply units. Specifically, in a manner similar to the firstembodiment, by making the powers generated across the power supplymodules in two power supply units connected to each other (for example,the power supply units Ub1 and U2) coincide with each other at the timeof discharging and regenerate charging, the powers generated across thepower supply modules of all of the power supply units can be equalized.

Therefore, when the capacities of all of the power supply modules 10 and40 constructing the power supply system are the same (when all of thepower supply modules are charged so as to be able to output the samepower) on start of driving of the power supply system of the fourthembodiment, at the time of discharging, the residual quantities of allof the power supply modules become zero at the same time so that a powersupply module having relatively low internal resistance and a powersupply module having relatively high output voltage (corresponding tothe module voltage Vmod) can be prevented from being over-discharged. Atthe time of regenerate charging, all of the power supply modules arefully charged at the same time point so that a power supply modulehaving relatively low internal resistance and a power supply modulehaving relatively low output voltage can be prevented from beingover-charged.

Even when a part of the power supply units U1 to Un and a part of thepower supply units Ub1 to Ubn are mixed, nothing is changed from thefirst embodiment for a load and a power supply for charging connected tothe pair of connection terminals (not shown in the fourth embodiment).Therefore, the power supply system of the fourth embodiment can realizeactions and effects similar to those of the power supply system 1 in thefirst embodiment. A power supply system constructed by mixing a part ofthe power supply units Ua1 to Uan in the second embodiment and a part ofthe power supply units Ub1 to Ubn in the third embodiment is similar tothe above.

Fifth Embodiment: Fuel Cell

A fifth embodiment of a power supply unit according to the presentinvention and a power supply system having the power supply unit will bedescribed below with reference to the drawings. The power supply systemof the fifth embodiment has, like the power supply system 1 of the firstembodiment shown in FIG. 1, “n” power supply units Uc1, Uc2, . . . , andUcn which are connected in parallel with one another (the power supplyunit Uc1 is shown in FIG. 8 but the other power supply units Uc2 to Ucnare not shown) and a pair of connection terminals (not shown) to which aload such as a motor is to be connected. That is, the connectionrelation of the “n” power supply units Uc1, Uc2, . . . , and Ucn issimilar to that of the “n” power supply units U1, U2, . . . , and Un ofthe power supply system 1 in the first embodiment.

FIG. 8: Description of Configuration

FIG. 8 shows the configuration of the power supply unit Uc1 of the fifthembodiment. Since the configuration of the power supply units Uc2 to Ucnother than the power supply unit Uc1 is similar to that of the powersupply unit Uc1, its illustration and description are omitted. In FIG.8, the same components are given the same reference numerals as those ofFIG. 2 and their description will not be repeated. The particular pointsdifferent from the first embodiment will be described below.

A power supply module 50 is constructed by a fuel cell (not shown) andoutputs power generated by the fuel cell to a load (not shown) connectedto the input/output terminals 11, 11 via two serial lines 52, 52. Thepower supply module 50 has therein parts (a pump and the like forsupplying hydrogen as the fuel of the fuel cell, which are not shown)enabling the fuel cell to output power. It is assumed that all of ratedoutput capacities of fuel cells in the power supply units Uc1 to Ucn arethe same and the output characteristic of each of the fuel cells issimilar to that shown in FIG. 9.

A point that the coil 131 as an inductor and the switching element 133for charging constructed by an MOSFET and a diode whose power supplymodule 50 side is an anode are provided for one of the two serial lines52, 52 is similar to the serial lines 12(FIG. 2). For one of the seriallines 52, 52, a diode 59 is further provided. More specifically, thepositive voltage output side of the power supply module 50 is connectedto the anode of the diode 59, and the cathode of the diode 59isconnected to the positive electrode of the second capacitor 134 andone end of the coil 131.

To the two serial lines 52, 52, a first voltage detection circuit 54 fordetecting a voltage across the power supply module 50 is connected, andthe second voltage detection circuit 15 for detecting the output voltageof the voltage increase/decrease circuit 13 is connected. Further, tothe two serial lines 52, 52, a current detection circuit 56 fordetecting current flowing in the power supply module 50 is connected.

The module voltage Vmod detected by the first voltage detection circuit54, the output voltage Vout detected by the second voltage detectioncircuit 15, and the module current Imod detected by the currentdetection circuit 56 are input to a discharge control circuit 57 builtwith a microcomputer. The discharge control circuit 57 calculates powergenerated across the power supply module 50 on the basis of the modulevoltage Vmod as a result of detection by the first voltage detectioncircuit 54 and the module current Imod as a result of detection of thecurrent detection circuit 56 at the time of discharging, and outputs thepower calculation result W to the power supply unit Ucn as one of thepower supply units connected as described above.

The operation of the discharge control circuit 57 is similar to that ofthe discharge/regenerate control circuit 17 in the first embodiment sothat more detailed description of the operation of the discharge controlcircuit 57 will not be repeated.

The discharging operation of the power supply system of the fifthembodiment is similar to that of the first embodiment. That is, in amanner similar to the first embodiment, by making the powers generatedacross the power supply modules 50 in two power supply units connectedto each other (for example, the power supply units Uc1 and Uc2) coincidewith each other at the time of discharging, the powers generated acrossthe power supply modules of all of the power supply units can beequalized.

Therefore, even if the output impedances of the fuel cells in the powersupply modules 50 are various, the powers generated across the powersupply modules 50 are equalized, and the risk of destruction of the fuelcells is extremely reduced.

In the power supply system of the embodiment, by changing the targetoutput voltage Vref, the power supply system of the embodiment can beused as a power supply source for various loads having different ratedvoltages. Particularly, when the load is a motor, a voltage which can beapplied to the motor can be freely set, so that the adjustment range ofthe motor rotational speed can be enlarged.

The power supply system of the embodiment can be used as a power supplysource of various loads having different power consumption byincreasing/decreasing the number (that is, the number indicated by “n”)of power supply units Uc1 to Ucn.

Even if a load tries to make the power regenerate to the power supplyunit Uc1 side, the power is prevented from flowing in the power supplymodule 50 by the diode 59. In the case where the load is not a loadhaving the nature of regenerating the power to the power supply unit Uc1side, the diode 59 can be omitted (the diode 59 can be short-circuited).

Variations and Modifications

Each of the configurations of the present invention is not limited tothe foregoing embodiments but can be variously modified within thetechnical range described in the scope of the claims.

For example, the on/off control of the switching element for dischargingand the switching element for charging can be realized not only bysoftware (such as the discharge/regenerate control circuit 17 or thecharge control circuit 18, which are built with a microcomputer) butalso hardware. The present invention is not limited to the voltageincrease/decrease circuits 13 and 33 shown in FIGS. 2 and 5 but canemploy various known voltage increase/decrease circuits.

Mixture of Different Specifications

In the first and second embodiments, a plurality of power supply moduleshaving the same capacity are used. It has been described that the powersupply modules are charged so as to be able to output the same power onstart of the driving of the power supply system. Alternatively, in thesame power supply system, power supply modules may be constructed byemploying secondary cells having quite different characteristics of therated capacity and the like.

In this case, it is sufficient to modify the configuration of theembodiments as follows. For example, in the first embodiment, when therated capacity of the power supply module 10 of the power supply unit U1is twice as large as that of the power supply module 10 of the powersupply unit U2 and the rated capacities of the power supply modules 10of the power supply units U2 to Un are the same, in the power supplyunit U1, it is sufficient for the power calculation circuit 173 tosupply, as the power calculation result W, a value obtained bymultiplying the product of the module voltage Vmod and the modulecurrent Imod with “½” as a computing factor to the power control circuit174 and the power supply unit Un connected (hereinafter, the control ofmultiplying such a computing factor will be referred to as “computingfactor adding control”).

In such a manner, the control of setting the power generated across thepower supply module 10 of the power supply unit U1 to a value which istwice as large as the power of the power supply unit U2 can be realized.At the time of discharging, the residual quantities of all of the powersupply modules become zero, and occurrence of a situation that a part ofthe power supply modules is over-discharged can be prevented. At thetime of regenerate charging, all of the power supply modules are fullycharged at the same time, and occurrence of a situation that a part ofthe power supply modules are over-charged can be prevented.

When a power supply module is constructed by a single secondary cell,the rated capacity of the power supply module 10 is equal to the ratedcapacity of the secondary cell. When a corresponding power supply moduleis constructed by a plurality of secondary cells, the rated capacity ofthe power supply module 10 is equal to a combined rated capacity of theplurality of secondary cells.

The “computing factor adding control” can be also similarly applied tothe third to fifth embodiments and it is sufficient to set the computingfactor in accordance with the electrostatic capacity of the powercapacitor constructing the power supply module and the rated outputcapacity of the fuel cell.

Current Balance Control

In each of the power supply units of the first to fifth embodiments, thecontrol of making the power of the power supply module coincide with thepower of the power supply module of the connected other power supplyunit is performed. Another configuration may be employed such that whenvariations of the output voltages of the power supply modules are small,a control of making the currents flowing in the power supply modulescoincide with each other (hereinafter, referred to as “current balancecontrol”) is performed.

The above will be described by using FIG. 3 in the first embodiment. Inthe power supply unit U1, the power calculation circuit 173 supplies asignal corresponding to the module current Imod in place of the powercalculation result W to the power control circuit 174 and the connectedpower supply unit Un. Further, the power control circuit 174 of thepower supply unit U1 receives a signal corresponding to the modulecurrent Imod of the power supply unit U2 supplied from the power supplyunit U2 in place of the power instruction Wref, and gives, in place ofthe power error signal Wref-W), a current error signal obtained bysubtracting the signal corresponding to the module current Imod of thepower supply unit U1 from the signal corresponding to the module currentImod of the power supply unit U2 to the error amplification circuit 172.

In such a manner, the control of making the module current Imod of thepower supply unit U1 coincide with the module current Imod of the powersupply unit U2 as one of the power supply units connected is performed,thereby equalizing the module currents Imod of the two power supplyunits U1 and U2 connected to each other. As a result, the modulecurrents Imod of all of the power supply units U1 to Un are equalized.Therefore, in the case where variations of the output voltages of thepower supply modules are small, the powers obtained from the powersupply modules become almost equal to each other, so that theabove-described various effects can be obtained.

Power Fixing Control

For example, only the power control circuit 174 (see FIG. 3) of thepower supply unit U1 among the power supply units U1 to Un in the firstembodiment may subtract the power calculation result W output from thepower calculation circuit 173 from a fixed power value Wfix.Specifically, the power control circuit 174 of the power supply unit U1may output a power error signal (Wfix-W) in place of the power errorsignal (Wref-W). Herewith, the powers generated across the power supplymodules 10 of all of the power supply units U1 to Un can be equalizedwith the predetermined power value Wfix at the time of discharging andregenerate charging. The fixed power value Wfix may be preset in thecontrol circuit 17 or given from the outside.

Such “a method of equalizing powers generated across all of the powersupply modules in the same power supply system with the fixed powervalue Wfix” can be also applied to the second to fifth embodiments.Particularly, in the case of applying the method to the fifthembodiment, by properly setting the power value Wfix, destruction of afuel cell which occurs when the fuel cell in the power supply module 50is over-discharged can be prevented with reliability.

The method of equalizing the powers generated across all of the powersupply modules with the fixed power value Wfix can be also combined withthe “current balance control”. Specifically, currents flowing in all ofthe power supply modules in the same power supply system may beequalized with a fixed current value Ifix.

1. A power supply unit having a pair of input/output terminals to/fromwhich power is to be input/output, and a power supply module to/fromwhich power can be input/output, the power supply unit comprising: avoltage detection circuit for detecting a voltage across the powersupply module; a current detection circuit for detecting current flowingin the power supply module; a voltage adjustment circuit for increasingthe voltage across the power supply module and outputting the increasedvoltage to the pair of input/output terminals or for decreasing thevoltage between the pair of input/output terminals and outputting thedecreased voltage across the power supply module; and a control circuitfor controlling operation of the voltage adjustment circuit, wherein thecontrol circuit includes: a power calculation portion for calculatingthe magnitude of a power generated across the power supply module on thebasis of a result of detection of the voltage detection circuit and aresult of detection of the current detection circuit; an output portionfor outputting a power calculation result of the power calculationportion to outside; and a control portion for generating a controlsignal on the basis of a target output voltage of the voltage adjustmentcircuit, the power calculation result of the power calculation portion,and a power calculation result obtained from outside, and for outputtingthe control signal to the voltage adjustment circuit.
 2. A power supplyunit having a pair of input/output terminals to/from which power is tobe input/output, and a power supply module to/from which power can beinput/output, the power supply unit comprising: a current detectioncircuit for detecting current flowing in the power supply module; avoltage adjustment circuit for increasing the voltage across the powersupply module and outputting the increased voltage to the pair ofinput/output terminals or for decreasing the voltage between the pair ofinput/output terminals and outputting the decreased voltage across thepower supply module; and a control circuit for controlling operation ofthe voltage adjustment circuit, wherein the control circuit includes: anoutput portion for outputting a current detection result of the currentdetection circuit to outside; and a control portion for generating acontrol signal on the basis of a target output voltage of the voltageadjustment circuit, the current detection result of the currentdetection circuit, and a current detection result obtained from outside,and for outputting the control signal to the voltage adjustment circuit.3. The power supply unit according to claim 1, wherein the power supplymodule is constructed by a storage battery or a capacitor.
 4. The powersupply unit according to claim 2, wherein the power supply module isconstructed by a storage battery or a capacitor.
 5. A power supply unithaving a pair of input/output terminals from which power is to beoutput, and a power supply module from which power can be output, thepower supply unit comprising: a voltage detection circuit for detectinga voltage across the power supply module; a current detection circuitfor detecting current flowing in the power supply module; a voltageadjustment circuit for increasing the voltage across the power supplymodule and outputting the increased voltage to the pair of input/outputterminals; and a control circuit for controlling operation of thevoltage adjustment circuit, wherein the control circuit includes: apower calculation portion for calculating the magnitude of a powergenerated across the power supply module on the basis of a result ofdetection of the voltage detection circuit and a result of detection ofthe current detection circuit; an output portion for outputting a powercalculation result of the power calculation portion to outside; and acontrol portion for generating a control signal on the basis of a targetoutput voltage of the voltage adjustment circuit, the power calculationresult of the power calculation portion, and a power calculation resultobtained from outside, and for outputting the control signal to thevoltage adjustment circuit.
 6. A power supply unit having a pair ofinput/output terminals from which power is to be output, and a powersupply module from which power can be output, the power supply unitcomprising: a current detection circuit for detecting current flowing inthe power supply module; a voltage adjustment circuit for increasing thevoltage across the power supply module and outputting the increasedvoltage to the pair of input/output terminals; and a control circuit forcontrolling operation of the voltage adjustment circuit, wherein thecontrol circuit includes: an output portion for outputting a currentdetection result of the current detection circuit to outside; and acontrol portion for generating a control signal on the basis of a targetoutput voltage of the voltage adjustment circuit, the current detectionresult of the current detection circuit, and a current detection resultobtained from outside, and for outputting the control signal to thevoltage adjustment circuit.
 7. The power supply unit according to claim5, wherein the power supply module is constructed by a storage battery,a capacitor or a fuel cell.
 8. The power supply unit according to claim6, wherein the power supply module is constructed by a storage battery,a capacitor or a fuel cell.
 9. A power supply system having a pair ofconnection terminals to which a load is to be connected, and having aplurality of power supply units connected in parallel with one anotherwith respect to the pair of connection terminals, each of the powersupply units comprising a power supply module capable of outputtingpower, each of the power supply units comprising: a voltage detectioncircuit for detecting a voltage across the power supply module of thepower supply unit itself; a current detection circuit for detectingcurrent flowing in the power supply module of the power supply unititself; a voltage adjustment circuit for increasing the voltage acrossthe power supply module of the power supply unit itself and outputtingthe increased voltage to the pair of connection terminals; and a controlcircuit for controlling operation of the voltage adjustment circuit, thecontrol circuits of all of the power supply units being connected toeach other or in an annular shape, wherein in each of the power supplyunits, the control circuit includes: a power calculation portion forcalculating the magnitude of a power generated across the power supplymodule in the power supply unit on the basis of a result of detection ofthe voltage detection circuit in the power supply unit and a result ofdetection of the current detection circuit in the power supply unit; anoutput portion for outputting a power calculation result of the powercalculation portion to a control circuit connected; and a controlportion for generating a control signal on the basis of a target outputvoltage of the voltage adjustment circuit in the power supply unit, apower calculation result of the power calculation portion in the powersupply unit, and a power calculation result obtained from the controlcircuit connected or another control circuit connected, and foroutputting the control signal to the voltage adjustment circuit in thepower supply unit.
 10. A power supply system having a pair of connectionterminals to which a load is to be connected, and having a plurality ofpower supply units connected in parallel with one another with respectto the pair of connection terminals, each of the power supply unitscomprising a power supply module capable of outputting power, each ofthe power supply units comprising: a current detection circuit fordetecting current flowing in the power supply module of the power supplyunit itself, a voltage adjustment circuit for increasing the voltageacross the power supply module of the power supply unit itself andoutputting the increased voltage to the pair of connection terminals;and a control circuit for controlling operation of the voltageadjustment circuit, the control circuits of all of the power supplyunits being connected to each other or in an annular shape, wherein ineach power supply unit, the control circuit includes: an output portionfor outputting a current detection result of the current detectioncircuit in the power supply unit to a connected control circuit; and acontrol portion for generating a control signal on the basis of a targetoutput voltage of the voltage adjustment circuit in the power supplyunit, the current detection result of the current detection circuit inthe power supply unit, and a current detection result obtained from thecontrol circuit connected or another control circuit connected, and foroutputting the control signal to the voltage adjustment circuit in thepower supply unit.
 11. The power supply system according to claim 9,wherein each of the power supply modules can also receive power and, ineach of the power supply units, the voltage adjustment circuit decreasesvoltage between the pair of connection terminals and outputs thedecreased voltage across the power supply module in the power supplyunit.
 12. The power supply system according to claim 10, wherein each ofthe power supply modules can also receive power and, in each of thepower supply units, the voltage adjustment circuit decreases voltagebetween the pair of connection terminals and outputs the decreasedvoltage across the power supply module of the power supply unit.
 13. Thepower supply system according to claim 11, wherein each power supplyunit has a pair of power input/output terminals connected to the pair ofconnection terminals, the voltage adjustment circuit includes: aninductor provided for one of two serial lines extending from both endsof a power supply module to the pair of power input/output terminals; aswitching element for charging provided on a power input/output terminalside of the inductor of the one serial line and having a rectifier forsetting a current direction at the time of discharging of the powersupply module to a forward direction; and a switching element fordischarging provided for parallel lines for connecting the two seriallines to each other between the inductor and the switching element forcharging and having a rectifier for setting the current direction at thetime of charging the power supply module to a forward direction, and thecontrol portion of the control circuit generates a control signal forthe switching element for charging and a control signal for theswitching element for discharging.
 14. The power supply system accordingto claim 12, wherein each power supply unit has a pair of powerinput/output terminals connected to the pair of connection terminals,the voltage adjustment circuit includes: an inductor provided for one oftwo serial lines extending from both ends of a power supply module tothe pair of power input/output terminals; a switching element forcharging provided on the power input/output terminal side of theinductor of the one serial line and having a rectifier for setting acurrent direction at the time of discharging of the power supply moduleto a forward direction; and a switching element for discharging providedfor parallel lines for connecting the two serial lines to each otherbetween the inductor and the switching element for charging and having arectifier for setting the current direction at the time of charging thepower supply module to a forward direction, and the control portion ofthe control circuit generates a control signal for the switching elementfor charging and a control signal for the switching element fordischarging.
 15. The power supply system according to claim 11, whereina charging power supply for supplying power to power supply modules ofthe plurality of power supply units can be connected to the pair ofconnection terminals, and each power supply unit has a charging controlportion for generating and outputting a control signal to the voltageadjustment circuit in the power supply unit itself on the basis oftarget input current of the power supply module of the power supply unititself and a detection result of the current detection circuit of thepower supply unit itself when the charging power supply is connected tothe pair of connection terminals.
 16. The power supply system accordingto claim 12, wherein a charging power supply for supplying power topower supply modules of the plurality of power supply units can beconnected to the pair of connection terminals, and each power supplyunit has a charging control portion for generating and outputting acontrol signal to the voltage adjustment circuit in the power supplyunit itself on the basis of target input current of the power supplymodule of the power supply unit itself and a detection result of thecurrent detection circuit of the power supply unit itself when thecharging power supply is connected to the pair of connection terminals.17. The power supply system according to claim 11, wherein a chargingpower supply for supplying power to power supply modules of theplurality of power supply units can be connected to the pair ofconnection terminals, and the control circuit of each power supply unithas charging control portion for generating and outputting a controlsignal to the voltage adjustment circuit in the power supply unit on thebasis of target input current of the power supply module of the powersupply unit and a detection result of the current detection circuit ofthe power supply unit when the charging power supply is connected to thepair of connection terminals.
 18. The power supply system according toclaim 12, wherein a charging power supply for supplying power to powersupply modules of the plurality of power supply units can be connectedto the pair of connection terminals, and the control circuit of eachpower supply unit has a charging control portion for generating andoutputting a control signal to the voltage adjustment circuit in thepower supply unit on the basis of target input current of the powersupply module in the power supply unit and a detection result of thecurrent detection circuit of the power supply unit when the chargingpower supply is connected to the pair of connection terminals.
 19. Thepower supply system according to claim 9, wherein the power supplymodule is constructed by a storage battery, a capacitor, or a fuel cell.20. The power supply system according to claim 10, wherein the powersupply module is constructed by a storage battery, a capacitor, or afuel cell.